1. Technical Field
The present invention generally relates to an encapsulation device and, more particularly, to an encapsulation device that is used to encapsulate a monitoring device typically used on the inner surface of a pneumatic tire to monitor tire conditions while the tire is mounted on a vehicle. Specifically, the present invention is related to a device for encapsulating an electronic monitoring device in a protective housing while allowing the pressure sensor of the monitoring device to remain in fluid communication with the surrounding atmosphere so that it may function.
2. Background Information
It is often desired in the art to monitor the conditions of a tire while it is installed and in use on a vehicle. Typical desirable measurements are tire wear, internal temperature, and internal pressure. These measurements are preferably taken while the tire is in use on a vehicle without having to remove the tire from the vehicle or specially position the tire to take the measurement. Numerous types of monitoring devices are known in the art to perform these measurements. One type of known monitoring device uses a passive integrated circuit embedded within the body of the tire that is activated by a radio frequency transmission that energizes the circuit by inductive magnetic coupling. Other prior art devices used for monitoring tire conditions include self-powered circuits that are positioned external of the tire, such as at the valve stem. Other active, self-powered programmable electronic devices are disclosed in U.S. Pat. Nos. 5,573,610, 5,562,787, and 5,573,611 which are assigned to the assignee of the present application.
One of the problems in the art with these monitoring devices is that they are relatively fragile when compared to the harsh environment of a pneumatic vehicle tire. The forces experienced by a pneumatic tire are sufficient to break the fragile electronic monitoring device and render it unusable. These forces include rotational forces caused by the rotation of the tire and shock forces caused by the tire impacting articles on the ground. It is thus necessary to provide the monitoring device with some protection from these forces. One manner of protecting the sensitive electronic monitoring device is to encapsulate the device in a relatively rigid material such as a hardened epoxy or plastic. The encapsulating material holds the elements of the electronic monitoring device in position with respect to each other and prevents the electronic monitoring device from tearing apart when subjected to the tire forces.
A problem with encapsulating the monitoring device is that the monitoring device preferably includes a pressure sensor that must remain in fluid communication with the internal cavity of the tire so that the pressure sensor may sense the internal pressure of the tire. The required fluid communication thus dictates that the entire electronic monitoring device cannot be encapsulated and that a breathing hole must be provided either during encapsulation or formed after encapsulation. Forming the breathing hole after encapsulation is generally not desired given the difficulty of precisely locating the hole, cleaning the pressure sensor, and the expense of the additional step in the encapsulation process. It is thus desired in the art to provide an encapsulation device that allows a monitoring device having a pressure sensor to be encapsulated while maintaining fluid communication between the pressure sensor and the surrounding atmosphere.
Another problem encountered with encapsulating an electronic monitoring device is that the monitoring device must be entirely encapsulated in preferably a single step. The monitoring device thus must float within the encapsulation chamber so that the encapsulation material may completely surround the encapsulation device. It is thus desired in the art to provide an encapsulation device that holds the monitoring device in a manner so that it may be entirely encapsulated in a single step.